Wrist devices for the manipulation of prosthetic limbs are known. In such devices, a prosthetic limb such as a prosthetic hand or digit is fixed to a support member which is pivobuttonly coupled to a base member. The base member is attached to a socket located on the wearer's residual limb or stump. The support member and hand can pivot relative to the base member in order to move the hand/digit into different positions.
An example of one such device is disclosed in US2007/0260328, in which a prosthetic hand and support member can pivot in a flexion/extension plane relative to a base member. A gear segment attached to the support member has a number of indentations which are engaged by resilient retention elements which hold the support member and hand in certain positions relative to the base member. The wearer pulls or pushes the prosthetic hand in the flexion/extension plane in order to move the hand to a new position. As this takes place the retention elements are forced out of their current indentations in the gear segment and will enter the adjacent indentations as the gear segment rotates. In addition to the retention elements a sliding locking device can be slid in and out of engagement with slots in the gear segment in order to lock the hand in a particular position. The locking device is biased into a locked position by a spring.
A similar arrangement is disclosed in U.S. Pat. No. 7,144,430, which also discloses an arrangement in which the hand and support member can be manipulated in both the flexion/extension and adduction/abduction directions about a form of universal joint. Torsion springs are provided which bias the hand into a neutral position. One or more spring-loaded locking pins engage the hand to lock it into positions along one or both of the flexion/extension and adduction/abduction axes.
In arrangements such as those referred to above, the prosthesis wearer can find it difficult to overcome the biasing forces of the resilient members or springs which hold the hand in position or force the hand towards a given position. Consequently, repeated movements of the hand about the wrist device can lead to fatigue in the wearer. In addition, the biased locking arrangements which lock the hand in a given position can be cumbersome and awkward for a wearer to actuate with their remaining natural hand, and even more so if they have another hand prosthesis.
It is an object of the present invention to obviate or mitigate one or more of these disadvantages.